High temperature transformer construction or the like



March 18, 1958 M, L, ANNING v 2,827,616

HIGH TEMPERATURE TRANSFORMER CONSTRUCTION OR THE LIKE NNNNNN OR MELVINL.MANNING f 0 2L 7 J5 I V M. L. MANNING March 18, 1958 HIGH TEMPERATURETRANSFORMER CONSTRUCTION OR THE LIKE Filed Aug. 6, 1952 2 Sheets-Sheet 2mv'EN'roR MELVIN L.MANNING naw/7 a4.

breakdown in that area.

invention.

United States Patent HIGH TEMPERATURE TRANSFORMER CONSTRUCTION OR THELIKE Melvin L. Manning, Upper St. Clair Township, Allegheny County, Pa.,assignor to McGraw-Edison Company (Pennsylvania Transformer Division), acorporation of Delaware Application August 6, 1952,.Serial No. 302,887

13 Claims. (Cl. 336-196) This invention relates to a new hightemperature transformer construction or the like. More particularly, itpertains to a new kind of transformer or the like in which silicone andfiber insulating materials are combined.

High temperature transformers and other high temperature electricalinduction constructions have been an objective of various manufacturersfor some time. The work in that direction received added impetus uponthe widespread introduction of silicone materials a few years ago.Despite the recognition of the electrical qualities of such materials, anumber of drawbacks attended use of them. One manufacturer despite theavailability of such silicone materials provided heat-resistant glasscylinders for insulating barriers.

I have discovered a new construction which enables the remarkableproperties of silicone materials to be fully employed for insulation andsupportpurposes to provide atransformer or the like with a class-Hrating. At the same time, I am enabled to shield the'leads and windingsby means of my new construction in a manner which preserves theadvantages thereof without risk of creepage or Other advantages of mynew construction are that it provides protection againstlocal dielectricand thermal weakness points and permitsefiicient construction practicestobe employed.

'Other objects and advantages of this-invention will be apparent fromthe following description and from the drawings, which are illustrativeonly, in which Figure 1 is a plan view, par'tly schematic,,of low andhigh voltage windings, barriers and spacers of a hightemperature drytransformer embodying my invention;

'Figure 2 is a view in elevation of the structureshown in Figure 1 takenalong line Til-11 of Figure 1;

Figure 3 is a somewhat detailed view of the portion of the. structureshown in, Figure l adjacent the low voltage transformer embodying my.invention in the course of being constructed.

Referring to the drawings, a .powertransformer is shown inFigureslan'dQZ in sufficientdetail to illustrate the new constructionfeaturesin one embodiment of my In that embodiment, acruciform laminatedcore leg 11 of a conventional magnetic core may be illustrated asshown-in Figure 1 by dot-and-dash lines. A core-.to low voltage windingv(CL) barrier envelope 12 surroundsxore'leg- 1 1 in close proximitythereto. Axial spacers 13 may be positioned around the outside of CL r 12,827,616 Patented M 1 barrier 12 in spaced arrangement where they areheld in the course of the winding of the concentric layers 14 and 15 ofa helically wound low voltage Winding. Spacers 13 may be held againstbarrier 12 by a suitable silicone adhesive or other means. Theconductors employedin winding the low voltage winding layers 14 and 15may be wire which is served with a glass silicone resin bonded tapeinsulation prior to winding. In other cases, such conductors may beserved with other materials such as flexible asbestos or glass clothsilicone tape or Teflon tape. Insulation in the form of a cylindricalenvelope 16 may be interposed between the layers 14 and 15 by using, forexample, silicone rubber ply material similar to that employed in theconstruction of CL barrier 12.

A further series of axial spacers 17 may be heldagainst and spacedaround the exterior of the low voltage winding coil comprising layers 14and 15. A further insulating (HL) barrier envelope 18 between the lowvoltage coil 14-15 and a high voltage coil 19 may be provided under mynew construction entirely of silicone and fiber matrix materials. HLbarrier 18 may comprise a combination of more of the interleaved pliesthan the numberused for the CLpbarrier as shown in Figure 6. Barrier 18insulates the low voltage windings from the high voltage windings andmust withstand the relatively high voltage potentials and thermalincreases to which it is subjected. A further series of axial spacers 20of solid or molded U shapes-may be fastened at uniform intervals aroundand to the exterior of HL barrier 18. Alternate spacers 21 in theseries-of spacers 20 may be of keytone shape, if desired, toperrnitkeying engagement with and movement during assembly for lateral spacers22.

The high voltage coil 19 may comprise a plurality-of double layerhorizontal pancake windings 23 in vertically stacked arrangement asshown in Figure 2, respective ones of said'suchwindingsbeinginterconnected electrically by .crossoverconductors 24. T he radialspacers 22 maybe ..cured to provide axial spacers ofmarkedly superiorme-.chanical and dielectric strengths.

The annular pressure plates and tie rods which respectively bearendwiseon the respective windings andlateralspacers 22 havenot been illustratedas suchfeatures willrbe wellunderstood by those skilled in the art. .The,verticalducts 25 between the axial spacers.13,the vertical ducts26between the axial spacers 17, the verticalducts 27 between theaxialspacers 21 and the lateral ducts 28between thelateralspacers 22afford access to the turns of the respective .windings for whatevercooling or ambient fluid may be employed. In

the case of a sealed dry-type transformer embodiment,,a gas likenitrogen may be used to fill the. gasspace within a transformer tank inwhich my new construction isplaced.

In construction the embodiment shownin Figures .1 and 2, one modeofmaking the new barrier envelopeis illustrate-d in connection with.making a barrier 18-.and other barrier 12 may be similarly made. Inthetransformer or thelike being constructed, any entire or other partialbarriers, whether cylindrical or arcuate, rnaybe constructed inaccordance with my invention. In that invention, one or more sheets 29of a formablesilicone resin and fiber laminate is combined ininterleaved manner with one or more plies 30 of flexible silicone rubberand fiber material. Generally, in preparing a cylindrical envelopebarrier in accordance with this invention, each kind of materialis'formed into the desired cylindrical shape beginning with theinnermost layer. Thus, a cylinder of the laminate may be provided andthe ends over- "one or more layers of the silicone rubber and fibermaterial may be formed in cylindrical shape around the laminate and theoutermost end of said material fastened again by silicone adhesive orother means. In some cases, the laminate material may have a siliconerubber -layer affixed to one or both surfaces of the laminate before thelaminate is formed. Around the silicone rubber and fiber material,another one or more layers of laminate material may be wound against theexterior of the silicone rubber and fiber material layer or layers tocomplete the interleaving. As shown in Figure 6, barrier 12,

for example, may be made in the form of a right cylinder, the innermostlayer of which as shown is a layer of formable laminate surrounded bytwo layers of silicone rubber and fiber in turn surrounded by a singlelayer of laminate again, the entire construction comprising a singlebarrier envelope with markedly superior features, both dielectricallyand mechanically, to any insulation heretofore provided.

The construction of a new barrier envelope may be performed in a windinglathe such as those used in the transformer industry. For example. asillustrated in Figure 7, a barrier such as HL barrier 18 is shown beingformed in place. The CL barrier has already been formed and is molded ina lathe 31 which rotates in the direction of the arrow. If desired, asteel cylinder may be used as the innermost mold to initiate theconstruction of barrier 12 thereagainst in which event a mold releasecompound, for example, may be used between the exterior of the moldcylinder and the interior cylindrical surface of the CL barrier 12.completed construction shown in Figure 7, the axial series of spacers 18has been positioned, the low voltage winding 1415 has been wound on thelathe around the spacers 13, the spacers 17 have been positionedand thelathe is in the midst of winding the HL barrier 18 as aforesaid with astrip 29 of laminate. Enough layers of silicone laminate and siliconerubber material Will be utilized in the new interleaved relation toprovide the necessary mechanical and dielectric strength required forthe high-low voltage barrier envelope service in the particulartransformer or the like under construction. When such winding of barrier18 is completed, that barrier, as is the case of barrier 12, will havesheets 29 and 3t) interleaved throughout. Preferably, the sheets 29 and30 are of a width equal to the entire height of the transformer windingsplus the additional height equal to the keep-back insulation lengthdesired at the respective axial ends of the transformer or the like.

The new construction of this invention also etfects a marked improvementin taking care of lead outlets particularly in the case of the moreinterior windings such as the low voltage coil 1415 shown in theillustrated embodiment. Leads 32 from the high voltage coil 19 do notgenerally present any particular problem in the case of an embodimentsuch as that shown because of their presence in the vicinity of theexterior of the transformer where they can, for example, be readilyconducted upwardly through an insulating tube, which, again, may be madeof tubular silicone material now available on the market. 7

On the other hand, conductor leads 33 are generally connected not onlyto the ends of the low voltage coil 1415 but also to intermediate pointstherein and'all of the leads or taps have to have an outlet from theinterior of the embodiment of the new transformer which is shown. In myinvention, cylindrical insulation plates 34 which arearcuate and may bepreformed of interleaved layers of laminate like laminate 29 alternatingwith interleaved layers of silicone rubber material like In thepartially ply 30 are provided and inserted in place as shown in Figures1 and 3' generally in the course of the construction winding as on lathe31. The surface of the insulation exposed to the lead or leads ispreferably faced with a silicone rubber coated glass cloth or asbestoscloth.

In such construction, as an example, the innermost plate 34- may bepinched between and held between the top turns of layer 14 and theadjacent axial spacers 13 on the other side of that plate 34. On theother hand, if keep-back insulation of a class-H category is interposedbetween the plates 34 above the topmost turn of the layers 14 and 15,and, on each side of leads 33. in a circumferential direction, as shownin Figure 3, then the plates 34 may respectively be held between suchkeepback insulation 35 and the axial spacers 13 and 20 respectively. Theheight of the plates 34 above the barriers 12 and 13 guards againstcreepage and any possibility of short-circuiting at the outlet shown ofthe taps 33 relative to parts of the transformer at diiferent voltagepotentials.

Laminate sheets such as sheets 29 may now be 'obtained as a commercialarticle having a fiber cloth matrix of an inorganic material likeheat-cleaned glass or asbestos. Such fibrous matrix in the case ofglass, for example, may be in part a staple cloth 36 woven of shortlengths of glass filaments in the manner of a staple'vegetable fibercloth. Laminate 29 also preferably employs a fiber matrix cloth 37 wovenof continuous glass filaments placed in juxtaposition to the cloth 36.These cloths 36 and 37 are impregnated with a silicone resin whichenters the interstices of the cloth and wholly covers them to form, whensolidified, the laminate sheets 29. In place of such fiber matrix, itmay also be possible to use such inorganic fibers in the form of afelted cloth or matte highly resistant to electrical, mechanical andthermal deterioration. The silicone resins may be of a kind such asthose sold by Dow Corning Corporation under the trade identification DC2104. A silicone ma terial laminate of suitable character for employmentin my invention is one such as that made by Mica Insulator Company ofSchenectady, New York, having the trade designation E-724 Lamacoid. Inpreparing laminate 29, usually from 40 to 60 percent of the weightthereof will be the partially or wholly cured and solidified siliconeresin. In applying the laminate 29, it is preferable to place the staplecloth 36 on the inside of the bend and the continuous fiber cloth 37 onthe outside, generally with the warp of both cloths parallel to thelongitudinal axis of the insulation envelope or cylinder beingconstructed.

Suitable silicone rubber plies such as the sheet 30 are also nowcommercially available on the market for employment in my invention.Such a silicone rubber material may comprise a cloth of inorganic fiberlike glass or asbestos, thoroughly heat-cleaned to remove organicbinders, which cloth forms a matrix for a silicone rubber coating. Onesuitable silicone elastomer for such coating purpose is Silastic, atrade name of Dow Corning Corporation, which corporation also makes asuitable silicone rubber and fiber matrix material suitable for thesheets 30. The fiber glass which may be utilized in the construction ofthe new insulation components of this invention should havecharacteristics suitable for satisfactory electrical, mechanical andthermal service in a class-H transformer. Certain of the glass productstermed Fiberglas by Owens Corning Fiberglas Corporation are suitable inmaking up the matrices for silicone sheet materials like sheets 29 and30.

In my employment of such new insulation in a transformer or the like, Ihave also found it useful to have the dielectric constants of theinterleaved sheet materials like sheets 29 and 30 of about the samedielectric constant, which may be in the neighborhood of 3.5. Thereby,the gradient through the materials in series because of theirinterleaved relation appears to be relatively uniform and the voltagestrength throughout the new insulation structitre will also be generallyuniform and foci of weakness for breakdown in the course 'of use areavoided. The use of various filler materials such as titanium dioxide orzinc oxide may be employed in the manufacture of the silicone rubbermaterial, as will be well understood by those in the art to whom thisinvention is disclosed, to achieve relative equality of the dielectricconstants of the component laminate and silicone rubber materials in thecomposite insulation. Other ways may be employed to harmonize therespective constants of the two sheet materials.

In constructing the new transformer the laminate may be formed cold forbent diameters exceeding about inches Whereas formerly it was believedthat such kind of material had to be beat formed. I find, however, thatnot only may such material be cold formed but that such cold forming forlaminates not in excess of about K of an inch in thickness does notproduce any tendency to craze it, particularly when used in cooperationwith a silicone rubber material like the sheets having a thicknessbetween about of an inch and of an inch. In some cases the laminate,particularly for smaller diameter uses or thicker sheets, may be heatedto about 165 C. for a relatively few minutes generally not in excess offour.

It appears that the new composite insulation forms a unitary mass whichfunctions ideally as the supporting framework for the windings of thenew transformer and provides dielectric characteristics and strengthbetween the variousparts of the transformer-at different potentials toenable a new transformer to function in the class-H category without thedisabilities of prior transformers in such category. The sheetm'aterials.29 and .30 so employed may in 'the case of the laminate bepartly or fully cured whereas in the case of the silicone rubber andfiber matrix material it will generally be in a partly cured state.Curing of the insulation after completion of the winding assemblies maybe performed at a temperature at about 250 C. Prior to such curing, thewinding assembly may be dipped into a silicone type of varnish, as oneexample, to complete the mechanical binding of the new transformerwindings and assembly. One advantage of such a varnish is that its highgloss reduces any opportunity for the settlement of dust or othercontaminant which might constitute a leakage path and another is itshigh craze resistance. Thereafter, if not earlier, any mold cylinderwhich has been employed will be removed before the completion andperformance testing of the entire transformer or the like.

A study of the advantages of my new composite insulation and cooperationin a transformer or the like leads to the belief that the interleavedsubstances complement one another in the course of use to a marked andunusual extent. For example, the silicone rubber and fiber matrixmaterial appears to at least hinder the aging of the silicone resin andfiber matrix laminate and also to cooperate in dissipating any tendencyto craze or crack which the laminate might otherwise have. Further, theheat conductive properties of the silicone rubber material appear to besuperior to those of a silicone laminate such as that described with theconsequence that the thermal lag of the one material like sheet 29 ismaterially aided if not overcome by the thermal conductivity of sheetmaterial like sheets 30. Thereby the new transformers or the like can beconsistently worked and operated at higher levels and/or for longertimes as in the case of varying load cycles or load demands ontransformers, without detriment.

The hot spot temperature standard of 180 C. set some years ago forclass-H insulation can be materially exceeded by means of the presentinvention without any observable deterioration. In constructing the newtransformer or the like, it will be understood that other insulatingmaterials that may be used for other parts of the transformer than thosedescribed herein will be of suitable electrical and mechanicalcharacteristics for the intended purpose. The invention is applicablenot only to dry but also to Wet transformers or the like and toventilated and sealed transformers and the like.

Various changes may be made in the practice of the present inventionwithout departing from the spirit thereof or the scope of the appendedclaims.

I claim:

1. In an electrical transformer, in combination, an at least partiallycured silicone resin impregnated insulating sheet having a heat-cleanedinorganic fiber base material and an at least partially cured siliconerubber insulating sheet having a heat-cleaned inorganic fiber basematerial, said sheets being contiguous and positioned between andinsulating portions of said transformer having a potential differencetherebetween, said fibers being selected from a group consisting ofglass and asbestos.

2. In a transformer, in combination, at least one formable siliconeresin impregnated sheet having a heatcleaned, continuous filament,inorganic fiber cloth, and at least one silicone rubber sheet having aheat-cleaned inorganic fiber cloth, said fibers being of a materialselected from a group consisting of glass and asbestos, said sheetsbeing contiguous and disposed between and insulating portions of saidtransformer having a potential difference therebetween.

3. In a transformer, in combination, a relatively thin, bendable, atleast partially cured silicone resin impregnated sheet havingheat-cleaned inorganic continuous filament and staple fiber cloths insuperposed relation, and a relatively thin, at least partially curedsilicone rubber sheet, said sheets being contiguous and positionedbetween and insulating portions of said transformer having "a potentialdifference therebetween.

4. In a transformer, in combination, an insulation barrier comprisingsilicone resin impregnated sheets interleaved with silicone rubbersheets, sai'd barrier being positioned between and insulating portionsof said transformer having a potential difference therebetween, saidsheets having approximately the same dielectric constant.

5. In a transformer, in combination, a bendable silicone resinimpregnated sheet having an inorganic heat resistant and electricallyinsulating heat-cleaned fibrous cloth, and a flexible, at leastparitally cured silicone rubber coated sheet having an inorganic heatresistant and electrically insulating heat-cleaned fibrous cloth, saidsheets being contiguous and positioned between and insulating portionsof said transformer having a potential difference therebetween, saidsheets further having approximately the same dielectric constant.

6. In an electrical transformer, the combination with a closed magneticcore having a winding leg and an electrical coil surrounding saidwinding leg of a tubular insulating barrier disposed between andinsulating said leg and said coil comprising interleaved at leastpartially cured silicone resin impregnated sheets having a heatcleaned,inorganic fiber, base material and at least partially cured siliconerubber sheets having a heat-cleaned, inorganic fiber, base material,said fibers being selected from a group consisting of glass andasbestos, said leg, said barrier, and said coil being bound together bya silicone varnish.

7. In an electrical transformer, the combination with concentric highand low voltage windings of a tubular insulating barrier interposedbetween and insulating said windings comprising interleaved siliconeresin impregnated sheets having a heat-cleaned, continuous filament,inorganic fiber cloth and silicone rubber sheets having a heat-cleanedinorganic fiber cloth, said fibers being of a material selected from agroup consisting of glass and asbestos, said barrier and windings beingbound together by a silicone varnish.

8. In an electrical transformer, the combination with congentricwindings ot-a tubular insulating barrier interposed'between andinsulating said windings comprising tormable silicone resin impregnatedsheets interleaved cylindrical winding and an arcuate insulatingbarrier, said barrier comprising silicone resin impregnated sheetsinterleaved Wtih silicone rubber sheets, each or" said sili- Qcone resinsheets having at least one heat-cleaned continuous filament cloth and atleast one heat-cleaned staple fiber cloth, said continuous filamentcloth being disposed radially outward from said staple fiber cloth andhaving its Warp parallel to the axis of said cylindrical winding, eachof said silicone rubber sheets having at least one heat-cleaned cloth,said cloths being of fibers selected from a group consisting of glassand asbestos, said barrier being adjacent said cylindrical winding andinsulating said winding from portions of said transformer at potentialsdiffering from that of said winding.

11; In an electrical transformer, the combination with concentricwindings of a tubular insulating barrier interposed between saidwindings, said barrier comprising silicone resin impregnated sheetsinterleaved with silicone rubber sheets, each of said resin impregnatedsheets having at least one continuous filament cloth and at least onedisposed radially outward from said staple fiber cloth and having thewarp thereof parallel to the axis of said tubular bairier, each of saidsilicone rubber sheets having at least one inorganic fiber cloth, saidcloths being of a material selected from a group consisting of glassfiber and asbestos fiber.

12. in stationary induction apparatus, in combination, at least onetormable silicone resin impregnated sheet having a heat-cleanedinorganic filler and at least one silicone rubber sheet having aheat-cleaned inorganic filler, said sheets being contiguous and disposedbetween and insulating portions of said stationary induction apparatushaving a potential difierence therebetween.

13. in an electrical transformer, the combination of a irical windingand an arcuate insulating barrier, said barrier comprising siliconeresin impregnated sheets interleaved with silicone rubber sheets, eachof said sheets having a heat-cleaned inorganic filler, said barrierbeing adjacent said cylindrical winding and insulating said winding fromportions of said transformer at potentials differing from that of saidwinding.

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